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In Focus - Archivo Abril 2012
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Flat workpieces can be easily, quickly and reliably clamped via underpressure on PLANOS matrix plates.
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01.04.2012 -
In comparison to clamping brackets, clamping blocks, jaw chucks, quick-change pallet systems, or magnetic clamping technology, vacuum clamping technology is mostly unknown in the metal cutting industry. Nevertheless, vacuum clamping technology can perform a valuable service here, especially when machining thin parts that are susceptible to deformation, or workpieces made of aluminum and other non-ferromagnetic materials. Particularly when they are in the form of versatile matrix plates, they are a useful and easy to handle addition to clamping devices already in use.
First a few basics on how vacuum clamping systems function. A vacuum occurs, according to DIN 28400, when the particle number density of a gas is lower than the particle number density of the atmosphere at the earth's surface, or, in other words, when the pressure of a gas is lower than the atmospheric pressure. It is precisely the pressure difference between the evacuated space below a workpiece and the natural atmospheric pressure above a workpiece that a vacuum clamping system uses to clamp workpieces. In contrast to the widely held belief that a workpiece is subject to suction when it is vacuum clamped, in fact the clamping force is created because the natural air pressure presses the workpiece evenly over its entire surface onto the clamping plate.
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If matrix plates are combined together, as here in this system for aircraft construction, long aluminum parts can be clamped without deformation.
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As a rule in the area of vacuum clamping technology, vacuum values are given in terms of the difference between ambient pressure and underpressure, and the ambient pressure is used as a reference point and is assumed to be 0 bar. Vacuum values also always have a minus sign in front of them, e.g. -0.3 bar (1 bar is equal to the force of 10 N on a 1 cm² surface). In order to determine the holding force (F) for a vacuum clamping system, the pressure difference (p) is multiplied by the effective surface (A). If for a 160 mm x 160 mm workpiece, a surface area of 150 mm x 150 mm is evacuated to -0.6 bar, the holding force (suction force) in the z-direction is F = 6 N/cm2 x 15 cm x 15 cm = 1350 N. Holding force and underpressure behave proportionally to one another. In contrast, the evacuation time as well as the energy required increase disproportionally if the underpressure and the holding force along with it are increased. In the above example, if the underpressure is increased by 1.5 times to -0.9 bar, the holding force increases proportionally to 2025 N. The energy required and the evacuation time increase disproportionally by a factor of 3.
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With the help of grid table suction devices, height differences can be compensated and cut-outs machined.
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The light matrix plates from SCHUNK can also be flexibly used on already existing clamping devices.
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Clamping of thin parts without risk of deformation
In the area of metal products cutting, vacuum clamping systems in the form of matrix plates whose base body consists of high-strength aluminum have proven to be optimal. They can be produced with standardized dimensions and grid dimensions of differing degrees of fineness. The clamping surface can be enlarged by connecting several matrix plates together. Based on the workpiece geometry, the machining and the horizontal forces, the suction surface and the necessary grid dimensions can be determined. The more fine the grid, the more complex the geometry of the workpieces can be.
In order to clamp a workpiece, a caulking strip that corresponds to the workpiece geometry is placed in the grid. Variable-use mechanical backstops make positioning easier and prevent the workpiece from shifting horizontally, for example during plane-milling. Subsequently the workpiece is placed down and the vacuum is activated. In a matter of seconds, the part is clamped down flat, securely and precisely. Height differences can be compensated via a so-called grid table suction device. With their help, cut-outs for the matrix plates can also be produced without risk.
Matrix plates are optimal for clamping thin workpieces. Even metal sheets can be mounted precisely and without risk of deformation. Clamping workpieces flat prevents vibrations and chatter marks from being caused. It is true, however, that in comparison to magnetic clamping plates, matrix plates have less holding force. Nevertheless, they can be used in the machining of non-ferromagnetic parts, such as workpieces made of aluminum or composite materials. Even thin plates or metal sheets, for which the magnetic field of magnetic clamping plates would provide no hold, can be reliably clamped with the help of matrix plates. Because of their comparably low weight, matrix plates can be used very well as an additional clamping solution. With the help of clamping blocks, clamping brackets, or magnetic clamping plates, they can be quickly and easily mounted to the machine table. For use as a quick change pallet system, they come from the factory partially threaded holes for clamping pins.
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Friction islands on
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Operation with a vacuum unit has advantages
In machining, in order to produce underpressure, two methods are used. Low-cost Venturi nozzles can be directly integrated into the matrix plates. They are compact, light, low-wear, develop no heat and make it possible to quickly generate a vacuum. However, they have a limited suction capacity, which means only completely sealed and relatively small surfaces can be clamped. Suctioned liquids can only be disposed of with difficulty with Venturi nozzles. In addition, the nozzles create a consistantly loud noise. Users who require a lot of flexibility and reliability usually decide for low-maintenance vacuum units, which are low-vibration and quiet-running and can be used with one or several matrix plates. High underpressures at simultaneously high volumetric flows can be produced with them. Vacuum units with an integrated reservoir provide a strong suction impulse and prevent a sudden drop-off of the vacuum. Ideally the units have various components for monitoring the system, and interfaces for integration in the machine control system. With special emergency stop functions, the vacuum pump is protected from being damaged by suctioned liquids, or stops the machine if there is sudden loss of clamping force.
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Friction islands off
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A sophisticated solution for workpiece clamping in the area of machining is the modular vacuum clamping system PLANOS from SCHUNK, whose vacuum unit has all of these safety features. Beyond that, the oil-lubricated vacuum pumps are equipped with a liquid separator, which also serves as a vacuum reservoir. A vacuum operation center makes it possible to automatically empty the unit during running operations if necessary, without interrupting the process. Since the vacuum pump is only activated when the vacuum falls below 85 %, the units are especially energy efficient and quiet. If necessary the control unit can be deactivated, so that the pump can be run in continuous operation mode. PLANOS matrix plates come in the following sizes, 300 x 200, 300 x 400 and 400 x 600 mm with grid dimensions of 12.5, 25 and 30 mm. Workpieces with a height tolerance of +/- 0.02 mm can be clamped on them. On request, the matrix plates from the competence leader for clamping technology and gripping systems can be equipped with patented friction islands. These are automatically activated via the vacuum supply and allow higher shearing forces. In comparison with matrix plates without friction islands, the horizontal holding forces increase by up to 30 % with friction islands. At the same time, this puts no additional force on the workpiece. The friction islands are oil and ozone-resistant and can be replaced individually if necessary. Matrix plates from by the innovative family-run company are often used as an additional clamping solution. As part of the worldwide largest modular program for stationary workpeice clamping, they can be mounted quickly and easily on already existing clamping devices, on MAGNOS magnetic clamping plates, for example, or on the VERO-S quick change pallet system.
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12.2012
New application possibilities for square pole technology
The electro-permanent square pole technology is a part of the magnetic clamping technology, and represents an ideal clamping solution for machining centers. It offers numerous advantages: Workpieces are easily accessible, and can be machined in one set-up from five different sides. It is no longer necessary to spend time on the fine adjustment of clamping elements. Multiple clamping operations of workpieces during the machining process are no longer necessary as well. In addition to milling applications, square pole technology also covers flat grinding applications. Moreover, special display modules increase process reliability and create optimum preconditions for automated loading.
 más…
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11.2012
High-performance automation from the modular system
Those who plan high-performance assembly plants for electronics, medical technology, automotive, or consumer goods industry, know of the challenges, if individual modules and assembly groups need to be linked to an entire system. Missing mechanical joining elements, incompatible controller concepts, or insufficient planning tools influence the planning and implementation processes as well as during the process itself. The variety of combinable system programs can be an efficient alternative - provided they are well thought out in terms of performance, volume, compatibility, and configuration.
más…
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10.2012
Applying strengths in a targeted way
Stationary clamping systems have enormous hidden efficiency and quality potentials for production. Those who want to utilize them, should question, where the strengths of the individual clamping technologies are. If they are selected and combined in a targeted manner, their investment costs can be amortized very quickly.
más…
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09.2012
The underestimated collaborators
In view of sophisticated lathe chucks, clamping blocks with compact performance, and highly engineered devices, the technological possibilities of chuck jaws may seem at the first glance rather limited. In reality, however, these direct interfaces to the workpiece open up enormous potentials: Beside conventionally hard and soft top jaws, a broad range of established chuck jaws ensure that even tricky clamping tasks can be economically solved. An overview shows what is potentially possible.
más…
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08.2012
Efficient concepts for automated machine loading
In the past, automated loading and unloading was restricted to large series, today though, small batches and individual pieces are now standard. The ultimate aim is to reduce set-up involved downtimes and to have as few workers possible manning production around the clock. What is needed, is the sophisticated interaction of innovative clamping equipment and automated components which lead to utmost precision and ensures reliable processes all at the same time.
más…
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07.2012
Consistent maintenance increases precision, process reliability,
and safety of the clamping vises in the long run
Vises used for workpiece clamping in today’s production environments are exposed to extreme conditions. This significantly influences the precision of the workpiece, process stability, and safety for both operator and machine. In order to ensure optimum clamping force, users normally follow the manufacturer’s information on lubrication intervals. Moreover, many more companies are choosing preventive maintenance programs, where the clamping vise is thoroughly tested in defined cycles. This ensures longtime accuracy, minimum wear, and high process reliability.
más…
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06.2012
High performance without chatter
The times when brachial roughing was normal are over. Those who want to produce a lot of chips in a short space of time now take advantage of high-quality cutting and intelligent toolholding systems that transmit high torques and, at the same time, reliably absorb any occurring vibrations. Modern toolholders protect the cutting edges, the machine spindle, and the workpiece surface and allow you to work with high metal removal rates even when using challenging materials.
más…
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05.2012
Pneumatic or mechatronic gripping?
In many industries, the increasingly wide range of product variants, the ever-shorter cycle of innovation, and the increasing comparability among products are leading to an enormous pressure on costs. Experts believe that production automation will be one of the keys to business success in the coming years. These issues also apply to gripping systems: the precision, flexibility, speed and reliability of a gripping system has a significant impact on the profit margin which they can achieve. Although pneumatic gripping systems were long considered the state of the art, mechatronic solutions have since made significant strides. As a result, users and system planners are increasingly faced with the question of which drive concept is more advantageous to handling and assembly processes: pneumatics or mechatronics?
más…
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04.2012
Vacuum clamping technology: an ideal addition to the standard clamping devices
In comparison to clamping brackets, clamping blocks, jaw chucks, quick-change pallet systems, or magnetic clamping technology, vacuum clamping technology is mostly unknown in the metal cutting industry. Nevertheless, vacuum clamping technology can perform a valuable service here, especially when machining thin parts that are susceptible to deformation, or workpieces made of aluminum and other non-ferromagnetic materials. Particularly when they are in the form of versatile matrix plates, they are a useful and easy to handle addition to clamping devices already in use.
más…
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03.2012
Gripping Systems of the future
Mechatronic handling systems offer distinct advantages: They are very flexible, offer numerous intelligent functions, and despite higher acquisition prices, they quickly pay off. Therefore, it is no surprise that the handling issue is becoming increasingly important in the pneumatics dominating world. This particularly applies, since more and more mechatronic components can be easily operated by average users.
más…
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02.2012
Tool extensions with minimal interfering contours
Due to the success of modern 5-axis machines, tool mountings with slim interfering contours have experienced a real boom. With sufficient torque, and high run-out accuracy they allow a deep, collision-free tool path into the workpiece, and thus ensure precision machining, even in areas which are difficult to access. These slim tool extensions are economic, flexible, and can be assembled between tool and toolholder on request. They can be combined with various machine tapers.
más…
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01.2012
Up-to-date support for all gripping tasks
Gripping systems in handling and assembly are often in operation around the clock, seven days a week. Many components have to withstand external influences such as chips, dust, aggressive media or heat. In addition, tight margins and deadlines due to just-in-time production often result in enormous scheduling and planning pressure, usually starting well before the initial commissioning. In view of these challenges, many purchasing decisions are increasingly made based not only on the quality and performance of the modules, but also on the range of services offered. Services increase planning reliability, facilitate commissioning and ensure maximum cost effectiveness during operation.
más…
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In Focus - 2013
In Focus - Archivo 2012
In Focus - Archivo 2011
In Focus - Archivo 2010
In Focus - Archivo 2009
In Focus - Archivo 2008
In Focus - Archivo 2007
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